In general, the invention relates to providing an atmospherically controlled sealed enclosure which permits economical staging access to and coating of exposed areas of ships' hulls of varying configurations both afloat and in drydock during the abrasive blasting, spray painting and solvent evaporation phases of the coating process so as to be, so far as practically possible, in full compliance with requirements of the U.S. Clean Air Act and Clean Water Act.
The present invention relates to apparatus and a method for surface work such as cleaning and painting, on exposed external surfaces of ship hulls, which improve upon the apparatus and methods which are disclosed in Garland et al., U.S. patent application 07/782,315, filed Oct. 24, 1991 (now U.S. Pat. No. 5,211,125, issued May 18. 1993) and in the copending U.S. patent application of Goldbach et al., application 07/975,520, filed Nov. 12, 1992 . now U.S. Pat. No. 5,355,823 issued Oct. 18, 1994. These are collectively referred to herein as the baseline apparatus and methods.
For disclosural purposes, the aforementioned U.S. patent applications are incorporated herein by reference.
Ship's hulls are very large and are complexly contoured in both the vertical and longitudinal directions. The world's population of ships has a very significant number of different sizes and shapes.
Coating of the exteriors of ships requires using abrasive blasters for surface preparation and painters for application of paint. Both blasters and painters must be brought into close proximity to the portion of the hull they are working. Neither blasters nor painters can perform their work on much more than 75 square feet of hull surface without moving or being moved to another location.
In earlier times, worker movement from place to place around a ship's hull was accommodated by building staging around the ship.
Also, in earlier times, the coating of the exterior hull above the waterline was most often done with the ship afloat. However, enactment in the U.S. of the Clean Water Acts all but eliminated this practice since coating of this area of a ship afloat deposited significantly more spent abrasive and paint overspray in the water than did coating in a drydock.
More recently, required worker movement has been accomplished through the use of manlifts. A conventional manlift includes a staging basket mounted on an arm which has the capability of being hydraulically lifted, extended and rotated; this arm being mounted on a carriage powered by an internal combustion engine. The carriage has the capability of being moved from place to place on a horizontal surface.
Even more recently for abrasive blasting, efforts have been made to replace the worker in the manlift basket, with an enclosed shotblast head which has the capability of catching, processing and reusing the abrasive. However, this approach has had little acceptance because of the cost to purchase and operate the apparatus, plus operating difficulties with the devices actually available.
Since ships are very large vessels which operate on large bodies of water, their construction and repair including drydocking almost always takes place immediately adjacent to large bodies of water.
Pollution of these large bodies of water including Great Lakes, rivers, seas, bays and oceans has become of much greater concern to societies around the world because of the negative effect of this pollution on the vegetable and animal life which depend upon these bodies of water. This concern has grown as more of the public elects to use these bodies of water for recreation through swimming and boating as well as living adjacent to them in hotels, houses, apartments and condominiums.
Abrasive blasting of a ship's hull necessarily creates a significant quantity of particulate material, usually dust comprised in part of smaller particles of the abrasive medium as it breaks down upon being propelled pneumatically against the ship's hull and in part of small particles of the ship's paint and steel which is removed by the abrasive. While this dust is not currently officially considered to be hazardous, it is nevertheless noxious to the public and does contain toxins in apparently nonhazardous quantities.
Because a portion of this dust inevitably is blown over the adjacent body of water, small quantities of these toxins find their way into the water. Further, if the large percentage of the spent abrasive which lands on the drydock floor is not promptly cleaned up, trace amounts of the toxins leach out during rainstorms or from other sources of water used in ship repair and are deposited into the body of water from the drydock's drainage system. Toxic petroleum products including fuels, lubricants and greases associated with manlift, forklift and compressor operations can similarly be carried through the drydock drainage system into the adjacent body of water.
Recent regulations implementing the U.S. Clean Water Act impose more stringent restrictions on contaminants in storm water runoff. These regulations mandate that either contaminants be eliminated or drydock storm water runoff be collected and treated, a process not currently feasible because of the quantity of water involved.
Typically, a ship has a large quantity of exterior mechanical equipment. This equipment, which is expensive to repair and purchase, is subject to severe damage if infiltrated by the dust from abrasive blasting, which is itself very abrasive. This mechanical equipment, which includes interior ventilation systems, must be temporarily covered with protective covering during abrasive blasting. This temporary covering inhibits operation of the interior ventilation systems when abrasive blasting is underway causing discomfort to ships crew members living aboard as well as to workers inside the ship.
Virtually all the equipment currently used in abrasive blasting has mechanical components. This includes air compressors, manlifts, forklifts, dust collectors and drydock cranes. Since this equipment must operate during abrasive blasting, it cannot be protected. It therefore, experiences very high maintenance cost, extensive out-of-service periods, and shortened operating lives.
Coatings on drydock horizontal surfaces experience short lives as they are abraded off by the combination of spent abrasive and vehicular and personnel movement, including that which accompanies shoveling and sweeping.
Workers who are free to proceed with exterior ship construction and/or repair tasks which do not involve mechanical ship's components are disrupted, made less efficient and exposed to respiratory and eye aggravation when abrasive blasting is proceeding concurrently. Workers and ship's personnel transiting through the abrasive dust cloud to and from the interior of the ship are similarly affected.
Most ships operate in a corrosive saltwater/spray environment. Therefore, the most popular marine paints are solvent-based vinyls and epoxies. Some marine paints contain zinc or copper. During the time that these paints are being applied, overspray is often blown into the adjacent body of water. This same overspray can coat itself on nearby boats, buildings, waterside cafes and cars, causing expensive damage and infuriating the public. Even the portion of the overspray which lands on the drydock floor can find its way back into the adjacent body of water as it attaches itself to dust or dirt particles on the floor of the drydock which are washed by water through the drydock's drainage system.
Non-waterbased paint solvents common in marine coatings release volatile organic compounds (VOCs) into the atmosphere during the time that they are evaporating, during the paint curing process. Regulatory authorities are becoming increasingly concerned that these VOCs are damaging the environment. While VOC emissions from marine paints may not be apparent to the public, they are a matter of growing regulatory oversight, and will ultimately have to be reduced. The only current way to dispose of these invisible VOCs is to contain the air into which they are released, and then process that air through a VOC incinerator.
Best management practices being currently utilized to minimize the amount of abrasive dust and paint overspray being blown beyond the drydock perimeter include placing a curtain over each end of the drydock, performing abrasive blasting downward only, using airless paint spray equipment, and ceasing operations when wind velocities become higher than a predetermined limit. However, these practices nevertheless permit a significant percentage of the airborne abrasive dust and paint overspray to blow outside of the perimeter of the drydock. In addition, these practices do nothing to reduce the many other negative affects of the ship coating process.
Recently, some shipyards have begun shrouding ships, from the weather deck down to the drydock structure, with very large strips of material. This material must be somewhat porous to keep it from shredding in the wind. However, the lives of these large strips of material are short because of damage from wind, handling, errant abrasive blasting and other hazards inherent to the heavy industrial environment prevalent in shipyards. Because of the basic cost of the shrouding material itself, its short life in the shipyard environment itself, the cost of installing, removing, handling and storing it, this approach is very expensive. While this approach contains even more airborne abrasive dust and paint overspray within the drydock perimeter than current generally accepted best management practices, some still escapes through the necessarily porous material and through the joints where the strips of material overlap. In addition, this approach does little to solve the many other negative effects of the ship coating process and does nothing to reduce VOC emissions.
One other technology exists that reduces dust from sandblasting, that is the technology of vacuum blasting. However, this process is very slow and very costly from an equipment and manpower standpoint and does not address painting problems including overspray and VOC emissions.
With regard to approaches to resolving the many problems associated with the coating of ships, as expensive as the coating process is or may become, the major cost consideration is the speed with which a ship may be coated or recoated. This is because of the daily amortization and operation costs of the drydock required to lift the ship out of the water for recoating ($5,000 to $20,000 U.S. per day) and the ship itself which is out of service during recoating ($10,000 to $100,000 U.S. per day). These costs demand that with whatever solutions are developed to solve the existing problems with abrasive blasting and coating of ships, elapsed time of the coating process be of the essence.
The first aforementioned copending U.S. patent application discloses a system for performing external surface work on a ship hull, in which a vertical tower is erected on a support surface beside a ship, e.g., on deck of a drydock in which the ship is berthed. A set of flexible confinement curtains externally surround the tower, but are open towards a vertical segment of the ship hull. The tower mounts a vertically movable trolley, to which a cantilever arm mechanism mounts a work platform. In use, workers and/or roboticly controlled devices operating from the platform use abrasive blasting (e.g., via compressed air-powered abrasive grit-spraying nozzles) and paint or other coating composition spray nozzles to work on the vertical segment of hull surface that is confined within the shroud provided by the curtains. A system of supply lines and recovery lines which extend into and out of the confined space supply air abrasive, paint and other needs, and collect fumes and other expended material for processing, reprocessing or disposal, all with the intent of minimizing contamination of the environment. Similarly, spent abrasive grit, with its burden of paint chips and scale fragments is swept-up for separation, reuse and disposal. As work on each vertical segment of the hull is completed, the tower is shifted to a successive location along the hull. Magnets mounted to edge portions of the curtains are used for removably fastening the front edge of the shroud to the ship hull around the whole of the perimeter of the respective vertical segment. During the course of the work on a segment, the work-applying nozzle is traversed horizontally while aimed at the hull, and after the particular act of work on each horizontal band of the segment has been completed, the trolley is raised or lowered on the tower, so that another band can be worked on. The cantilever arms which mount the work platform to the trolley are extended and retracted, as needed, for maintaining the desired proximity of the work-applying nozzle to the hull surface from one band to the next. Although the baseline apparatus and method as disclosed in this aforementioned U.S. patent contemplate that more than one tower may be in use at the same time for performing respective tasks on respective vertical segments of the same ship hull, this aforementioned U.S. patent does not disclose jointly shrouding plural ones of the towers.
However, this latter improvement is a main topic of the second aforementioned copending U.S. patent application. The baseline apparatus and method as disclosed in that application discloses simultaneously working on adjoining segments of the same hull using a plurality of towers having respective adjustably cantilevered, elevatable work platforms, with the shroud curtains possibly providing interconnected confined spaces for all or some of the towers, with some side curtains subdividing the space in order to isolate the environments of various types of work from one another, as needed. That aforementioned U.S. patent application further discloses providing a support barge for carrying the various air compressors, paint supply tanks, abrasive material hoppers, so that all of these items of equipment need only to be connected to the various nozzles, etc., within the shrouded, confined space, rather than individually transferred to, from and from place to place around the hull. Other elaborations are disclosed, including possibly stationing the towers on a movable barge, so that the above-waterline part of a floating ship can be worked upon using the apparatus and method. In that connection, towers which can be laid-down for transit on their support barge, then easily erected to vertical positions for use are disclosed, as are ways and means for connecting the tower-support barge to the floating ship, and for using inflatable seals and also dams to seal the front edges of the shroud curtains to the hull, and bottom edges of the shroud to the support deck despite possible relative movement of the ship and tower support barge, and for reducing run-off of spent abrasive, paint particles and removed scale from the tower support deck to the body of water around the floating ship, or ship in drydock which is being worked-on.
In practicing the baseline apparatus and methods, as well as those of the present invention, it is a goal to provide sufficient freedom of motion to permit full worker and/or robotic access to all of the external surface of the ship hull that is to be worked on, and also to contain abrasive blast dust, spent abrasive, paint overspray and volatile organic compounds (VOCs), thereby significantly reducing the quantities of these materials which are released to contaminate the air, nearby bodies of water, ship's mechanical equipment, drydock cranes, abrasive blasting and painting support mechanical equipment, local housing, automobiles, nearby yachts and other floating vessels, and in addition significantly reduce the efforts necessary to collect, dispose of, recycle and incinerate waste abrasive and paint residue and significantly reduce the disruption of the concurrent shipboard repair work, all without increasing the drydock utilization times or ship out-of-service times.
For assisting a reader who does not have ready access to the disclosure provided in the above-mentioned copending U.S. applications, most of the detailed description which is provided in most extensively in the second of them and that is substantially germane to preferred practices of the present invention, are repeated below with reference to FIGS. 1-14.
Preferred practices of the baseline apparatus and methods made possible significant improvements in environmental compliance during ship hull coating because of the following:
a. Use of internal combustion equipment is eliminated with its potential to pollute the water through fuel oil, lubricating oil and grease spills which run or wash off the drydock floor.
b. Abrasive dust is collected and processed without leaving the enclosure.
c. Paint overspray is filtered without leaving the enclosure.
d. VOCs are contained and incinerated without leaving the enclosure.
e. Storm water is prevented from running through spent abrasive and debris contaminated with paint.
f. Use of recyclable steel grit abrasive instead of mineral abrasive eliminates disposal of spent abrasive with its contained toxins.
Preferred practices of the baseline apparatus and methods also provided a significant opportunity for improvement in coating quality by preventing negative effects of weather by preventing rain or snow from impacting on hull areas during coating and by providing hotter dehumidified air during coating.
Preferred practices of the baseline apparatus and methods further provided a significant opportunity to shorten coating and drydock span times by:
a. Shortening or eliminating equipment mobilization, setup, teardown and demobilization time through use of the coating support barge.
b. Eliminating weather interruptions.
c. Accelerating paint curing by heating air in the enclosure.
d. Allowing most ship repair work to proceed during hull coating.
e. Reducing drydock cleanup time by confining contaminated or spent abrasive to within the enclosure.
Preferred practices of the baseline apparatus and methods further facilitated very considerable reductions in the cost of the coating process for all the reasons respectively listed immediately previously under opportunities to reduce coating and drydock span times. Even more significant cost reductions can be realized as the very significant costs associated with drydock utilization and ship out-of-service times reduce proportionately to span time reductions. Also:
a. Rework from weather can be eliminated.
b. Transportation and crane handling of support equipment can be eliminated.
c. Abrasive contamination maintenance of manlifts, cranes, forklifts and compressors can be eliminated.
d. Wear and tear on portable hoses and ducting can be virtually eliminated.
e. Temporary covering of ship's mechanical equipment can be eliminated.
f. Purchase and disposal of mineral abrasive can be eliminated.
The present invention builds on the advantages provided by preferred practices of the baseline apparatus and methods, and, in preferred practices thereof, provides additional advantages.
The present invention provides certain improvements on the baseline apparatus and methods, that grew out of experiences with building and operating prototypes of such baseline apparatus and methods, and the making of plans for larger scale, commercial use of such apparatus and methods for performing external surface work on ship hulls.